Infrared double resonance of SiH4 with a tunable diode laser: Two-photon absorptions and rotational relaxation times

Millot, Guy; Hetzler, J.; Foy, Bernard R.; Steinfeld, J. I.

doi:10.1063/1.454418

Cited by 22 publications

(2 citation statements)

References 25 publications

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“…This suggests that it is mainly the diagonal anharmonicity, x 44 , that tunes ν 4 in the vibrationally pre-excited molecule in resonance with the dissociating frequency, although we cannot rule out the case in which the off-diagonal anharmonicities are significant but coincidentally equal. The results of double resonance spectroscopy of ν 4 suggest a value of 2.2 cm -1 for the x 44 anharmonic constant, which implies that on the order of two quanta in the ν 4 mode would be enough to bring the P(10) transition of the ν 4 band into resonance with the 868 cm -1 dissociating frequency allowing molecules pre-excited to J = 10 to be efficiently dissociated via IRMPE. This same dissociating frequency would be off-resonant for molecules pre-excited to other rotational states.…”

Section: Discussionmentioning

confidence: 99%

Collision-Free Infrared Multiphoton Dissociation of Silane

2000

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We have measured an upper limit of 17 J/cm2 for the threshold fluence for collision-free CO2 laser IRMPD of silane by detecting the SiH2 product in its electronic and vibrational ground state. The threshold drops to ∼4 J/cm2 when silane molecules are irradiated by all lines from a pulsed NH3 laser. This value further drops to less than 2 J/cm2 when the molecules are pre-excited to the first Si−H stretch overtone. Using the NH3 laser on the 868 cm-1 line, the dissociation yield of pre-excited SiH4 reaches saturation at a laser fluence of 6 J/cm2. The substantial difference in the fluence threshold and optimal dissociation frequency of the ground and excited molecules allows us to perform highly selective dissociation of pre-excited silane in the presence of a large excess of ground-state molecules.

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Section: Discussionmentioning

confidence: 99%

Collision-Free Infrared Multiphoton Dissociation of Silane

2000

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“…Our inability to find signal on the R(0) line points to nuclear spin selectivity in our jet, similar to the propensities observed in rotational energy transfer in silane. 52,53 Because Q-branch excitation averages over a number of rotational lines, all of which have similar ␤ axis values, the S fwd ͑2͒ value measured by Q-branch excitation is probably more reliable. Rotational alignment also may have some subtle effect on the steric measurement.…”

Section: ͑5͒mentioning

confidence: 99%

Reaction of Cl with vibrationally excited CH4 and CHD3: State-to-state differential cross sections and steric effects for the HCl product

Simpson

Rakitzis

Kandel

et al. 1995

The Journal of Chemical Physics

234

201

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Thermal and vibrationalstate selected rates of the CH4+Cl↔HCl+CH3 reaction J. Chem. Phys. 103, 9642 (1995); 10.1063/1.470731Core extraction for measuring statetostate differential cross sections of bimolecular reactionsThe mechanism for the reaction of atomic chlorine with vibrationally excited methane is investigated by measurement of correlated state and scattering distributions using the method of core extraction ͑see preceding paper͒. Laser photolysis of molecular chlorine creates monoenergetic chlorine atoms ͑Ͼ98% Cl 2 P 3/2 ͒ that react with vibrationally excited methane molecules prepared by linearly polarized infrared laser excitation. The resulting HCl product population distributions are determined by ͑2ϩ1͒ resonance-enhanced multiphoton ionization ͑REMPI͒, and the differential cross section for each product rovibrational state is measured by core extraction. Approximately 30% of the product is formed in HCl(ϭ1,J) with a cold rotational distribution; the remaining population is formed in HCl(ϭ0,J) and is more rotationally excited. We observe a rich variation of the scattered flux that is dependent on the internal-energy state of the product. The HCl͑ϭ1͒ product is sharply forward scattered for low J and becomes nearly equally forward-backward scattered for high J; the HCl(ϭ0,J) product is back and side scattered. The reactions of Cl with C-H stretch-excited methane ͑CH 4 ͒ and C-H stretch-excited CHD 3 are found to have similar angular and internal-state distributions. Observation of the spatial anisotropy of the HCl͑ϭ0, Jϭ3͒ product shows that significant vibrational excitation of the methyl fragment does not occur. The measured spatial anisotropy is most consistent with a model in which backscattered HCl͑ϭ0, Jϭ3͒ is formed in coincidence with slight methyl vibrational excitation and the forward-scattered HCl͑ϭ0, Jϭ3͒ is formed in coincidence with no methyl excitation. The approach of the attacking chlorine atom with respect to the C-H stretch direction can be varied by rotating the plane of polarization of the infrared excitation. A marked steric effect is observed in which Cl atoms approaching perpendicular to the C-H stretch preferentially yield forward-scattered HCl͑ϭ1͒ product. On the other hand, the reaction is weakly dependent on the rotational quantum state of CH 4 ( 3 ϭ1,J), and on the rotational polarization. The data are consistent with a model that has a widely open ''cone of acceptance'' in which the impact parameter controls the internal-state and scattering distributions of the HCl product.

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Measurments of collisional line widths in the stimulated Raman Q‐branch of the ν₁ band of silane

Millot

Boutahar

Lavorel

et al. 1990

J Raman Spectroscopy

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Self-broadened widths of '%iH, in the v1 @branch have been measured at room temperature (295 K) using high-resolution stimulated Raman spectroscopy. These collisional widths have been obtained by fitting a superposition of Voigt profiles to the experimental spectra in the pressure range 28-154 Torr. No evidence for line mixing within the tetrahedral components of a Q(J) line has been found. The l i e broadening coefficients for J up to 13 depend weakly on the rotational quantum number. The mean value is 103.7 x cm-' atm-'.

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Infrared double resonance of SiH4 with a tunable diode laser: Two-photon absorptions and rotational relaxation times

Cited by 22 publications

References 25 publications

Collision-Free Infrared Multiphoton Dissociation of Silane

Collision-Free Infrared Multiphoton Dissociation of Silane

Reaction of Cl with vibrationally excited CH4 and CHD3: State-to-state differential cross sections and steric effects for the HCl product

Measurments of collisional line widths in the stimulated Raman Q‐branch of the ν₁ band of silane

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Infrared double resonance of SiH4 with a tunable diode laser: Two-photon absorptions and rotational relaxation times

Cited by 22 publications

References 25 publications

Collision-Free Infrared Multiphoton Dissociation of Silane

Collision-Free Infrared Multiphoton Dissociation of Silane

Reaction of Cl with vibrationally excited CH4 and CHD3: State-to-state differential cross sections and steric effects for the HCl product

Measurments of collisional line widths in the stimulated Raman Q‐branch of the ν1 band of silane

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Measurments of collisional line widths in the stimulated Raman Q‐branch of the ν₁ band of silane